1. Field of the Invention
One disclosed aspect of the embodiments relates to a display apparatus, and more particularly, to a display apparatus using an organic electroluminescence (EL) display element.
2. Description of the Related Art
To represent a gradation in an image displayed on an active matrix organic electroluminescent display apparatus, it is known to divide one frame period into a plurality of subframe periods, and rewrite data on a subframe-by-subframe basis while scanning each frame. U.S. Pat. No. 7,113,154 discloses a subframe-controlled gradation representation technique in which a display scan for writing data and an erase scan for erasing are performed such that periods thereof are overlapped to achieve a light emission period with a length shorter than the length of one scan period. U.S. Pat. No. 7,129,918 discloses a technique in which when two or more scan periods overlap each other, a scan selection period of one line is divided into as many intervals as there are overlapping scans. Data is generated in each interval, and a selection pulse for selecting one scanning line is applied in each interval. More specifically, in a case where two display scans overlap each other, a scan selection period of each line is divided into two intervals. In each interval, data is applied to data lines and a selection signal is applied to a scanning line. In a case where a display scan and an erase scan overlap each other, display data is applied in one interval, and erase data is applied in the other interval.
In the technique in which scan periods overlap, each scan selection period is divided into a plurality of intervals and one scanning line is selected in each interval, the number of intervals increases with the number of overlapping scans, and a corresponding increase occurs in the scan selection period length. As a result, a corresponding increase occurs in the length of a period from a start to an end of scanning.
The length of one frame period is determined by a frequency at which one frame of image data is input to the display apparatus. Therefore, the increase in the length of the period necessary for the display scan results in a decrease in the number of subframes in one frame, which results in a decrease of the number of gradation levels that may be displayed.